1. Field of the Invention
The present invention relates to a belt for a continuously variable transmission, which is reeved around a drive pulley and a driven pulley to transmit a driving force in a state in which a metal ring assembly has been supported in a ring slot defined in a large number of metal elements, and the adjacent metal elements have been positioned by fitting of a projection and a recess with each other.
2. Description of the Prior Art
In a belt for a continuously variable transmission described in Japanese Patent Application Laid-open No. 7-12177, the rolling of a metal element short of a location where it bites into a pulley from a chord of the metal belt is restricted by limiting the clearance between an outer peripheral surface of a metal ring assembly and a lower ear surface, thereby preventing the occurrence of the wearing and a reduction in transmitting efficiency due to the incorrect meshing engagement of the metal elements with the pulley.
In a belt for a continuously variable transmission described in Japanese Patent No. 2,617,784, the length of a pulley-abutment face of a metal element put into abutment against a V-groove of a pulley and the shape of a radially inner end of the pulley-abutment face are defined based on the relationship between an angle of inclination of the V-groove of the pulley and a pitch width of the metal element (a lateral width on a pitch line), so that even when the metal element bits into the pulley in a rolling state, a saddle face of the metal element does not exceeds a reference height, thereby preventing an excessively large load being applied to a metal ring assembly.
However, the belt described in Japanese Patent Application Laid-open No. 7-12177 suffers from a problem that when the driving of the belt has been conducted for a long time, a particular portion of an outer peripheral surface of the metal ring assembly, which strongly abuts against the lower ear surface, is damaged due to the fatigue. This results in a reduction in durability of the entire metal belt, because the rolling of the metal element is restricted by the abutment of the outer peripheral surface of the metal ring assembly and the lower ear surface of the metal element against each other.
The belt described in Japanese Patent No. 2,617,784 suffers from the problem that when the driving of the belt has been conducted for a long time, a particular portion of an outer peripheral surface of the metal ring assembly, which strongly abuts against the saddle face, is damaged due to the fatigue. This results in a reduction in durability of the entire metal belt, because the rolling of the metal element is restricted by the abutment of the inner peripheral surface of the metal ring assembly and the saddle face of the metal element against each other.
Accordingly, it is an object of the present invention to enhance the durability of the metal ring assembly by inhibiting the rolling of the metal element without recourse to the abutment of the metal ring assembly and a ring slot against each other.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided a belt for a continuously variable transmission, comprising a large number of metal elements, each of which is provided with a front main face and a rear main face capable of being brought into contact with an opposing face of an adjacent metal element, a ring slot provided between a saddle face connecting the main faces to each other and a lower ear surface. A projection is provided on one of the front and rear main faces to protrude therefrom, and a recess is formed on the other of the front and rear main faces and into which the projection can be loosely fitted. The belt is adapted to be reeved around a drive pulley and a driven pulley to transmit a driving force between both of the pulleys in a state in which the large number of metal elements are supported via a metal ring assembly in the ring slot, wherein when the metal element is rolled relative to the metal ring assembly, the outer peripheral surface of the projection comes into abutment against the inner peripheral surface of the recess, before the inner peripheral surface of the metal ring assembly comes into abutment against the saddle face and the outer peripheral surface of the metal ring assembly comes into abutment against the lower ear surface.
With the above arrangement, when the metal element immediately upstream of the metal element positioned correctly the moment it bites into V-grooves of the pulley is being rolled relative to the downstream metal element, the lower ear surface of the downstream metal element can be prevented from coming into abutment against the outer peripheral surface of the metal ring assembly by restricting the maximum angle of rolling of the downstream metal element relative to the upstream metal element which are fitted with each other via their projection and recess, thereby enhancing the durability of the metal ring assembly. When left and right pulley-abutment faces bite into the left and right V-grooves incorrectly in a state in which the downstream metal element is being rolled, the downstream metal element can be restored to a correct attitude under the action of a load generated by the abutment of the projection and the recess against each other. At this time, the lower ear surface of the downstream metal element is not put into abutment against the outer peripheral surface of the metal ring assembly and hence, it is possible to prevent a reduction in durability of the metal ring assembly.
According to a second aspect and feature of the present invention, the relationship of xcex8NH less than xcex8Y is established between the following two angles: (1) an angle xcex8Y formed between a straight line drawn from a lower end of one of the left and right pulley-abutment faces of the metal element to a laterally outer end of the other of the left and right lower ear surfaces and a straight line drawn from the point of intersection of a straight line drawn down radially inwards from the laterally outer end of the other lower ear surface with the outer peripheral surface of the metal ring assembly to the lower end of the one pulley-abutment face; and (2) an angle xcex8NH formed between a tangent line drawn from the lower end of the one pulley-abutment face of the metal element onto the outer peripheral surface of the projection and a tangent line drawn from the lower end of the one pulley-abutment face of the metal element onto the inner peripheral surface of the recess.
With the above arrangement, the angle xcex8Y formed between the straight line drawn from the lower end of one of the left and right pulley-abutment faces of the metal element to the laterally outer end of the other of the left and right lower ear surfaces and the straight line drawn from the point of intersection of the straight line drawn down radially inwards from the laterally outer end of the other lower ear surface with the outer peripheral surface of the metal ring assembly to the lower end of the one pulley-abutment face is set larger than the angle xcex8NH formed between the tangent line drawn from the lower end of the one pulley-abutment face of the metal element onto the outer peripheral surface of the projection and the tangent line drawn from the lower end of the one pulley-abutment face of the metal element onto the inner peripheral surface of the recess. Therefore, the outer peripheral surface of the projection can reliably come into abutment against the inner peripheral surface of the recess, before the inner peripheral surface of one of the left and right ends of the metal ring assembly contacts the saddle face and the outer peripheral surface of the other end of the metal ring assembly comes into abutment against the lower ear surface.
According to a third aspect and feature of the present invention, there is provided a belt for a continuously variable transmission, comprising a large number of metal elements, each of which is provided with a front main face and a rear main face capable of being brought into contact with each other. A ring slot is provided between a saddle face connecting the main faces to each other and a lower ear surface, a projection is provided on one of the front and rear main faces to protrude therefrom, and a recess is formed on the other of the front and rear main faces, into which the projection can be loosely fitted. The belt is adapted to be reeved around a drive pulley and a driven pulley to transmit a driving force between both of the pulleys in a state in which the large number of metal elements have been supported via a metal ring assembly in the ring slot. The relationship of xcex8NH less than xcex8Y is established between the following two angles: (1) an angle xcex8Y formed between a straight line drawn from a lower end of one of the left and right pulley-abutment faces of the metal element to a laterally outer end of the other of the left and right lower ear surfaces and a straight line drawn from a point of intersection of a straight line drawn down radially inwards from the laterally outer end of the other lower ear surface with the outer peripheral surface of the metal ring assembly to the lower end of the one pulley-abutment face; and (2) an angle xcex8NH formed between a tangent line drawn from the lower end of the one pulley-abutment face of the metal element onto the outer peripheral surface of the projection and a tangent line drawn from the lower end of the one pulley-abutment face of the metal element onto an inner peripheral surface of the recess.
With the above arrangement, the angle xcex8Y formed between the straight line drawn from the lower end of one of the left and right pulley-abutment faces of the metal element to the laterally outer end of the other of the left and right lower ear surfaces and the straight line drawn from the point of intersection of the straight line drawn down radially inwards from the laterally outer end of the other lower ear surface with the outer peripheral surface of the metal ring assembly to the lower end of the one pulley-abutment face is set larger than the angle xcex8NH formed between the tangent line drawn from the lower end of the one pulley-abutment face of the metal element onto the outer peripheral surface of the projection and the tangent line drawn from the lower end of the one pulley-abutment face of the metal element onto the inner peripheral surface of the recess. Therefore, the outer peripheral surface of the projection can reliably come into abutment against the inner peripheral surface of the recess, before the inner peripheral surface of one of the left and right ends of the metal ring assembly contacts the saddle face and the outer peripheral surface of the other end of the metal ring assembly comes into abutment against the lower ear surface.
Thus, when the metal element immediately upstream of the metal element positioned correctly the moment it has bitten into V-grooves of the pulley is being rolled relative to the downstream metal element, the lower ear surface of the downstream metal element can be prevented from being put into abutment against the outer peripheral surface of the metal ring assembly, thereby enhancing the durability of the metal ring assembly. When the left and right pulley-abutment faces bite into the left and right V-grooves incorrectly in a state in which the downstream metal element is being rolled, the downstream metal element can be restored to a correct attitude under the action of a load generated by the abutment of the projection and the recess against each other. At this time, the lower ear surface of the downstream metal element is not put into abutment against the outer peripheral surface of the metal ring assembly and hence, it is possible to prevent a reduction in durability of the metal ring assembly.
According to a fourth aspect and feature of the present invention, the metal element has a pair of the left and right ring slots, which are supported on a pair of the left and right metal ring assemblies, respectively.
According to a fifth aspect and feature of the present invention, the projection and the recess are provided on a centerline of the metal element.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.